Stubbs is a host

I don't think so, not because it's not possible, but because it doesn't add anything to the story

I do think Stubbs has been around the park long enough to recognize the older hosts, whatever form they may take. Meaning: I think Stubbs recognized Dolores in her Charlotte-Hale-suit, or at least very strongly suspected Hale was a host imposter. Tessa Thompson appeared to be acting very Dolores-like at that point.

I haven't gone back through the series yet, but wasn't Dolores-as-Charlotte keeping Stubbs occupied throughout the series run? She seemed to mainly be interacting with Strand & Costa.

He could also have been using those terms metaphorically. You could practically hear the scare quotes around "core drive."

Personally I don't think it's an interesting reveal, precisely because his job is so mechanical. But it does explain how he was able to sniff out Dolores in Charlotte's body.

It could also be argued that Bernard never had a bomb implanted in her neck when he created her, which I believe is what they scan for.